The MCG database contains the "Morphological Catalogue of Galaxies," a compilation of information for approximately 34,000 galaxies found and examined on the Palomar Observatory Sky Survey (POSS). Individual identifiers are assigned for about 29,000 galaxies and information on the remaining 5,000 is present in the extensive notes of the published catalogs (Vorontsov-Velyaminov et al. 1962-1968). The catalog is structured according to the POSS zones and is numbered from +15 (corresponding to +90 deg) to +01 (+06 deg zone) and +00 (equatorial zone) to -05 (-30 deg zone); the fields are numbered with increasing right ascension. The original goal of the compilation was to be complete for galaxies brighter than magnitude 15.1, but the final catalog lists many objects considerably fainter. Information given in the original printed volumes includes: cross- identifications to the NGC (Dreyer 1888) and IC (Dreyer 1895, 1908) catalogs, equatorial coordinates for 1950.0, magnitude, estimated sizes and intensities of the bright inner region and the entire object, estimated inclination, and coded description (by symbols) of the appearance of the galaxy. Each field is then followed by notes on individual objects. All of the above data except the coded description are included in the machine version, except that special coding (e.g. for uncertainty or source designation) is not present (other than for the NGC/IC cross identifications [added at the Astronomical Data Center for this machine version]). Although the notes are not computerized, the presence of a note in the original is flagged in the machine version Detailed descriptions of modifications, corrections and the record format are provided for the machine-readable version of the "Morphological Catalogue of Galaxies" (Vorontsov-Velyaminov et al. 1962-68); see the Additional Information section below. In addition to hundreds of individual corrections, a detailed comparison of the machine-readable with the published catalog resulted in the addition of 116 missing objects, the deletion of 10 duplicate records, and a format modification to increase storage efficiency. This is a service provided by NASA HEASARC .